1. Field of the Invention
The present invention relates to an apparatus for dispensing active substances or materials, and in particular to a portable spraying apparatus having an oscillating fire burner which operates with pulsating combustion and has an oscillating tube, a tank for the active material and a discharge line connected thereto, and a fuel reservoir which feeds the burner via a suction line.
2. Description of the Prior Art
With one known apparatus of this type, the active material is atomized by means of a pulsating gas column in the oscillating tube and is then ejected from the latter. The fuel is hurled backwards from the oscillating tube during the backward oscillations, is collected in a turbulence chamber, and is thereafter hurled back again from this chamber. The excessive pressure formed during the repulsion of the pulsating gas column in the turbulence chamber is passed into the fuel reservoir, so that a pressure builds up therein. The feeding of the fuel into a mixing neck of the oscillating fire burner, in which the fuel is mixed with air, is effected as a function of this pressure. The fuel/air mixture is ignited in the following combustion chamber. At the end of the oscillating tube, there is fed to the pulsating gas mixture the active material, which is usually mixed with water or oil. Since these carrier media for the active material are cooler than the hot pulsating gas column, heat is extracted from the latter, causing the pulsating frequency of the gas column to drop. Since the oscillation system has been set at no-load, that is to say without the supply of any active material, in such a way that the gas column operates at maximum pressure in the resonance range, the pressure drops as a result of the heat extraction. This also causes the output of the apparatus to be reduced. The constant flowing-in of the active material furthermore causes the mass of the gas column to be increased, which may also lead to disturbance of the inherent frequency of the gas column. These mechanical and thermodynamic influences cause the gas column to be removed from the resonance range to such a considerable extent that the apparatus gets out of step or cycle, causing the active material to be no longer dispensed in a uniformly distributed manner. The reduction of the frequency of the gas column leads to a pressure drop in the oscillation system, and consequently to a reduction of the fuel supply. The apparatus is then interrupted because the fuel supply is too low, and therefore has to be re-started, which is complicated and leads to an undesirable loss of time, the more so since the apparatus is intended for continuous operation.
An object of the present invention is to develop an apparatus of the aforementioned general type in such a way that the impairment of the frequency of the gas column as a result of the active material input does not affect the operation of the apparatus nor the active material discharge.